Electrolytically refining silver.



No. 795,887. PATENTED AUG. 1. 1905.

' A. G. BETTS.

ELEGTROLYTIGALLY REPINING SILVER.

APPLICATION FILED MAR. 8. 1905.

ANDREW u mm mm :0 Wk) ml 111 100mm u .ua wmlmmv. n, v.

"UNITED STATES PATENT OFFICE.

ELECTROLYTl CALLY REFINING SILVER.-

ivo. 795,887.

Specification of Letters Patent.

Patented Aug. 1, 1905.

Application filed MarchB, 1905- Rferial No. 249,054.

in vertical cross-section of an electrolytic c'ell for carrying out my invention.

This invention relates to the use of solutions-of silver salts of strong non-oxidizing, preferably monobasic, acids, as electrolytes for electrolytically refining silver alloys.

Certain objects of my invention are to produce a silver deposit on the cathodes of such solidity that the electrolytic refining opera tion and apparatus are respectively facilitated and improved, and to effect the solution'of antimony, bismuth, and such usually undesirable elements of the anodes with the silver.

Other objects may be noted in the following description.

Such objects are achieved by using in the electrolytes strong non-oxidizing acids, and, further, by. the addition of small amounts of certain substances, as gelatin and gum-arabic. These substances should most suitably be present between the proportions of one part to twelve thousand solution and one part to fifteen thousand. The presence of oxidizing compounds nitric acid, for example is found to prevent the action of the gelatin or gum in preventing the growth of the deposits on the cathodes toward the anodes. An especiall y suitable solution contains four per cent. silver, as silver methyl sulfate, and four per cent. of methyl sulfuric acid. hen silver has been reduced to one and one-half per cent. from the presence of lead, copper, or bismuth in the anodes, the solution should be removed and replaced by fresh solution. Other suitable acids are fluoboric, alkyl sulfonic, and sulfuric acids, and aromatic sulfonic acids.

Dithionic acid gives good results, as it is a strong acid, somewhat stronger than sulfuric acid; but the results with any dibasic acid are distinctly inferior to those obtained with monobasic acids of the strongest order, such as I have mentioned.

The electrolysis may be ery well carried on with a current density of ten amperes per square foot cathode surface for as long a time as the high value of silver under treatment makes economical-say forty eight hours without the least danger of short-circuiting from the growth of trees. The deposit is not perfectly solid and can be easily scraped off the cathode sheets, which I have found to be an advantage rather than otherwise, for the cathode sheets may be used over and over again. No silver falls from the cathodes into the tanks or when removing them, unless it is knocked off with some instrument.

No necessity exists for wrapping silver anodes in cloth, as in hitherto used electrolytic parting processes, for whether the anode slime, mostly of gold, drops from the anodes or remains sticking to them it cannot become mixed with the cathode silver.

A particular advantage in using strong nonoxidizing monobasic acids is that they dissolve large quantities of their bismuth salts, and a considerable excess of free acid does not cause any action on the electrodes beyond the electrolytic action. The bismuth accumulating in the solution I can precipitate with hydrofluoric acid, as bismuth fiuorid, or after precipitating silverfor instance, with metallic bismuthby precipitation with metallic lead. If the latter method is adopted, the resulting lead solution can be treated with finelydivided silver sulfate, precipitating lead sulfate and regenerating silver solution to be used over again:

Having reference to the accompanying drawing, 1 is a tank containing the electrolyte 2.

In the electrolyte are suspended anodes 3 of silver containing impurities and cathodes 4, on which is the pure electrodeposited silver 5.

What I claim as new, and desire to secure by Letters Patent, is

1. The process of electrolytically refining silver which consists in subjecting the silver alloy as anode to an electric current in an electrolyte containing a free,non-oxidizing,strong acid forming a readily-soluble silver salt, and the silver salt of said acid, and electrolytically depositing the silver on a suitable cathode.

2. The process of electrolytically refining silver which consists in subjecting the silver alloy as anode to an electric current in an electrolyte containing a free, non-oxidizing, monobasic strong acid forming a soluble silver salt, and the silver salt of said acid, and electrolytically depositing the silver on a suitable cathode.

3. The process of electrolytically refining silver which consists in subjecting the silver alloy as anode to an electric current in an electrolyte containing, a free, non-oxidizing, monobasic strong acid forming a soluble silver salt, the silver salt of said acid, and an agent to hinder the growth toward the anode of the cathode deposit of silver, and electrolytically depositing the silver on a suitable cathode.

4. The process of electrolytically refining silver containing bismuth which consists in subjecting the silver alloy as anode to an electric current in an electrolyte containing a free, non-oxidizing, monobasic strong acid, the silver salt of said acid, and an agent to hinder the growth toward the anode of the cathode deposit of silver, and electrolytically depositing the silver on a suitable cathode; and recovering from the electrolyte the bismuth dissolved from the anode.

5. The process of electrolytically refining silver containing bismuth which consists in subjecting the silver alloy as anode to an electric current in an electrolyte containing a free, non-oxidizing, monobasic strong acid, the silver salt of said acid, and an agent to hinder the growth toward the anode of the cathode deposit of silver, and electrolytically depositing the silver on a suitable cathode; and recovering by precipitation with metallic lead, the bismuth dissolved from the anode.

6. The process of electrolytically refining silver containing bismuth which consists in subjecting the silver alloy as anode to an electric current in an electrolyte containing a free, non-oxidizing, monobasic strong acid, the silver salt of said acid, and an agent to hinder the growth toward the anode of the cathode deposit of silver, and electrolytically depositing the silver on a suitable cathode; recovering bismuth dissolved from the anode from the electrolyte by precipitation with metallic lead, precipitating lead from the electrolyte, dissolving silver in the electrolyte, and using the thus regenerated electrolyte in electrolytically refining silver.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

ANSON GARDNER BETTS.

Witnesses:

LIVERMAN P. SHOTTEN, EDWARD F. KERN. 

